Computer graphics systems are commonly used for displaying graphical objects on a display screen. These graphical objects include points, lines, polygons, and three dimensional solid objects. Using techniques well known in the art, color and surface details can be added to areas and surfaces of objects. One particularly useful technique for adding surface detail to areas or surfaces is texture mapping. Using texture mapping, a pattern image or texture map is combined with an area or surface of an object thereby producing a modified object with the added detail of the texture map. For example, given a flat black solid cube and a texture map defining a wood grain pattern, the texture mapping technique can be used to map the wood grain pattern onto the cube thereby producing a cube that appears to be made of wood. The texture mapping technique is particularly useful as surface detail becomes finer and more intricate thereby rendering the use of geometric primitives less practical.
Texture mapping operates by applying color or visual attributes of point elements (texels) of a texture map to corresponding point elements (pixels) of an object on a display screen. As long as the coordinate system of the texture map is positioned or in some way related to the coordinate system of the object being textured, the association between texels and pixels is well defined. A problem, however is present in prior art systems when an object or portion of an object extends beyond the coordinate range of the texture map. This may occur if the scaling between the texture map and the object does not allow coverage of the entire surface of the object by the texture map. In this situation, the object is out of range of the texture map and the association between texels and pixels is no longer well defined. Many prior art systems handle the out-of-range situation by simply repeating the texture map pattern if an out-of-range condition is encountered. In these systems, the texture map space wraps around in both dimensions thereby creating an endlessly repeating texture map. In many situations, however a repeated texture pattern is not desirable. For example, a product manufacturer may want to visualize a packaging label as it would appear on a proposed product container. In this case, a repeated label pattern (i.e. texture) as provided by prior art systems would not be a realistic portrayal of the actual finished product. In another example, a texture map comprising far more texels than can be conveniently stored in mapping hardware, such as photo-derived terrain, is used for applying texture to a ground surface. A better method is needed to extend the coordinate range of the texture mapped to such an object.
It is therefore an object of the present invention to provide a technique for applying a texture to an object where the coordinates for the object are outside the coordinate range of an associated texture map. It is further an object of the present invention to provide a means for suppressing the application of texture to an object for specified object coordinate range.